Oil-based pigmented ink composition

ABSTRACT

An oil-based pigmented ink composition containing a pigment, a polymer and an organic solvent, wherein the organic solvent contains a (poly)alkylene glycol derivative in an amount of 30 to 90% by weight and a nitrogen-containing heterocyclic compound in an amount of 1 to 30% by weight, each based on the whole weight of the ink composition, and the ink composition has a flash point of at least 63° C.

FIELD OF THE INVENTION

[0001] The present invention relates to an oil-based pigment compositioncomprising a pigment, a polymer (a pigment-dispersant and/or a fixingresin), and an organic solvent, in particular, an oil-based pigmentcomposition for ink-jet printing systems.

PRIOR ART

[0002] In an ink-jet printing system, a liquid ink is ejected from anozzle towards a recording medium using a pressure, heat or an electricfield as a driving source to print the recording medium. The ink-jetprinting system can be used with a low running cost and form highquality images. Furthermore, this printing system can use various inkssuch as aqueous and oil-based inks. Accordingly, the ink-jet printingsystem has been expanding its market.

[0003] Under such circumstances, large-size inkjet printers, which canbe used to print a sheet of the A-0 size with aqueous pigmented inks,have been developed, and are used to output indoor posters, CAD(computer aided drawing) drawings, or proofing for color matching inprinting. The printed materials can be used outdoors with laminatingthem.

[0004] Furthermore, the demand for outdoor use of the ink-jet printedmaterials has been increased. Therefore, oil-based pigmented inks aredeveloped, which can be printed directly on films of polyvinyl chloride(PVC) and used outdoors without lamination, and have good waterresistance and weather resistance.

[0005] Since the oil-based pigmented inks comprise organic solvents assolvents, they do not cause the cockling of a paper sheet in comparisonwith aqueous pigmented inks, or require no lamination of a film having areceptive layer. Therefore, they can be printed on a substrate at lowcost.

[0006] For example, JP-A-10-077432 discloses an oil-based pigmented inkcomprising a glycol solvent having a boiling point of at least 150° C.and a specific polyester resin. However, since this ink does not containa solvent in which polyvinyl chloride dissolves, it is not well fixed ona film of, for example, PVC.

[0007] JP-A 2002-302629 discloses an oil-based pigmented ink comprisinga solvent having a boiling point of at least 200° C. and a specificresin. However, when a glycol solvent having a boiling point of at least200° C. is used as a single solvent, the ink has low fixing propertieson a PVC film. When a ketone solvent is used, the ink has problems suchthat it is flammable or it emits a foul odor.

[0008] Apart from those oil-based pigmented inks, as an aqueouspigmented ink comprising an aqueous solvent, JP-A 2002-363468 disclosesan aqueous pigmented ink comprising N-methyl-2-pyrrolidone as ahumectant. However, this aqueous ink may not be well fixed on a film of,for example, PVC.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide an oil-basedpigmented ink, which has high safeness and low odor which are importantfor an oil-based pigmented ink, can be printed on an inexpensiveprinting medium such as a PVC film having no receptive layer, and canendure outdoor environment.

[0010] To achieve the above object, an extensive study has been made andit has been found that when a (poly)alkylene glycol derivative and anitrogen-containing heterocyclic compound such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, etc. are used incombination as the organic solvents of an oil-based pigmented inkcomposition, the ink composition has high safeness and low odor, can beprinted on an inexpensive printing medium such as a PVC film having noreceptive layer, and can satisfactorily endure outdoor environment, andin particular, the ink composition is suitable for ink-jet printingsystems.

[0011] Accordingly, the present invention provides an oil-basedpigmented ink composition comprising a pigment, a polymer and an organicsolvent, wherein the organic solvent contains a (poly)alkylene glycolderivative in an amount of 30 to 90% by weight and a nitrogen-containingheterocyclic compound in an amount of 1 to 30% by weight, each based onthe whole weight of the ink composition, and the ink composition has aflash point of at least 63° C.

[0012] Since the oil-based pigmented ink composition of the presentinvention contains the (poly)alkylene glycol derivative and thenitrogen-containing heterocyclic compound such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, etc. in combination asthe organic solvent, the odor, which is one of the problems of theconventional oil-based pigmented ink compositions, can be improved, theink composition can be printed with good fixing and drying properties ona film of PVC having no receptive layer. Furthermore, the inkcomposition of the present invention can form a printed material havinggood resistance to water and alcohol. In particular, the ink compositionof the present invention is suitable for ink-jet printing systems. Sincethe ink composition of the present invention has a flash point of atleast 63° C., it can reduce the danger in transportation and handling.

DETAILED DESCRIPTION OF THE INVENTION

[0013] In the oil-based pigmented ink composition of the presentinvention, the organic solvents essentially contain a (poly)alkyleneglycol derivative and a nitrogen-containing heterocyclic compound.

[0014] When the ink composition containing the above combination of thesolvents is printed on a printing medium having no ink-receptive layer,in particular, the PVC film, the solvents partly dissolve PVC and thusthe fixing of the ink on the film is enhanced. In addition, most of thenitrogen-containing heterocyclic compounds do not violate the regulationfor preventing poisoning with organic solvents in the Industrial Safetyand Health Law so that they are very safe, and they have low odor.Accordingly, the ink composition containing the nitrogen-containingheterocyclic compound has high safeness and low odor.

[0015] Examples of solvents in which PVC dissolves include ketones (e.g.acetone, methyl ethyl ketone, cyclohexanone, etc.), oxygen-containingheterocyclic compounds (e.g. tetrahydrofuran, etc.), nitrogen-containingheterocyclic compounds (e.g. pyrrolidone, etc.), and so on.

[0016] Among them, the ketones and tetrahydrofuran have goodPVC-dissolving power. However, acetone, methyl ethyl ketone, methylisobutyl ketone, methyl n-butyl ketone, cyclohexanone,methylcyclohexanone, tetrahydrofuran, etc. are designated in theIndustrial Safety and Health Law. A material containing 5% by weight ormore of one of them can be handled by a person having a specialqualification, and a person who handles such a material should get amedical checkup. Therefore, the handling of those solvents istroublesome.

[0017] Among the ketones and tetrahydrofuran derivatives other than theabove compounds, ketones and tetrahydrofuran derivatives having a lowmolecular weight may well dissolve PVC, but many of them have a lowflash point so that it is highly possible that ink compositionscomprising such solvents have a flash point of lower than 63° C.Furthermore, since such solvents have strong odor, the ink compositioncontaining only a slight amount of the solvent may emit odors. Ketonesand tetrahydrofuran derivatives having a high molecular weight have ahigh flash point and low odor. However, such solvents less dissolve PVCand thus the pigments in the ink composition may not be sufficientlyfixed to the substrate.

[0018] The nitrogen-containing heterocyclic compounds are heterocycliccompounds having at least one nitrogen atom in a ring, and most of themdo not violate the regulation for preventing poisoning with organicsolvents in the Industrial Safety and Health Law as described above.Therefore, they are highly safe, and emit less odor. Accordingly, inkcompositions comprising such heterocyclic compounds have good safenessand low odor. That is, the nitrogen-containing heterocyclic compoundshave much better properties as organic solvents of the ink compositionsthan the oxygen-containing heterocyclic compounds such as ketones ortetrahydrofuran.

[0019] Examples of the nitrogen-containing heterocyclic compoundsinclude 2-pyrrolidone and its derivatives, in particular,N-alkyl-2-pyrrolidone such as N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone,N-cyclohexyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, etc.

[0020] Among them, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone arepreferable, since they have low odor and good fixing properties.

[0021] The nitrogen-containing heterocyclic compound is usuallycontained in an amount of 1 to 30% by weight, preferably 5 to 28% byweight, more preferably 15 to 25% by weight, based on the whole weightof the ink composition. When the amount of the nitrogen-containingheterocyclic compound is less than 1% by weight, the ink composition maynot sufficiently dissolve PVC. When the amount of thenitrogen-containing heterocyclic compound exceeds 30% by weight, theeffect to dissolve PVC will be saturated, and the volatility of the inkcomposition becomes insufficient so that printed characters or imagestend to drip or blur.

[0022] To qualitatively and quantitatively analyze thenitrogen-containing heterocyclic compound in the ink composition, gaschromatographic mass spectroscopy (GCMS) is advantageously used.

[0023] The (poly)alkylene glycol derivative, which is another essentialcomponent of the organic solvent according to the present invention, hasa polar group (i.e., an ester group and an ether group) and ahydrophobic group (i.e., an alkyl group) in the molecule. Therefore,when the (poly)alkylene glycol derivative is used as one of the primarysolvents, it is possible to formulate an ink composition which exhibitsgood fixing properties and water resistance not only on the PVCsubstrate but also any other printing medium such as a plain paper, amatte paper, a glossy paper, etc. The fixing properties, waterresistance as well as the odor and flash point of the ink compositioncan be easily controlled by selecting the number of the ester and ethergroups and the number of carbon atoms in the alkyl group.

[0024] In view of the safeness and odor of the ink composition, the(poly)alkylene glycol derivative preferably has a flash point of 70 to120° C., more preferably 80 to 100° C., and preferably a boiling pointof 170 to 250° C.

[0025] When the (poly)alkylene glycol derivative is used in combinationwith the nitrogen-containing heterocyclic compound, the flash point ofthe ink composition as a whole can be easily set to 63° C. or higher sothat the ink composition has very high safeness with regard to theignition during transportation of the ink composition.

[0026] Examples of the (poly)alkylene glycol derivative includecompounds having one free hydroxyl group such as a monoalkyl ether or amonoalkyl ester of a (poly)alkylene glycol, etc., and compounds havingno free hydroxyl group such as a monoalkyl ether monoalkyl ester, adialkyl ether or a dialkyl ester of a (poly)alkylene glycol, etc.

[0027] Among them, the compounds having no hydroxyl group such as themonoalkyl ether monoalkyl ester, the dialkyl ether and the dialkyl esterare preferable since they can decrease the viscosity of the inkcomposition and improve the water resistance of the ink composition.Among the alkyl esters, those having a methyl ester group arepreferable.

[0028] Examples of the monoalkyl ether monoalkyl ester of a(poly)aklylene glycol include ethylene glycol monoalkyl ether monoalkylester, diethylene glycol monoalkyl ether monoalkyl ester, triethyleneglycol monoalkyl ether monoalkyl ester, propylene glycol monoalkyl ethermonoalkyl ester, dipropylene glycol monoalkyl ether monoalkyl ester,tripropylene glycol monoalkyl ether monoalkyl ester, and so on.

[0029] Among them, di- or trialkylene glycol monoalkyl ether monoalkylester is preferable since it has a larger molecular weight, a higherflash point and boiling point, and lower odor than monoalkylene glycolmonoalkyl ether monoalkyl ester.

[0030] In particular, diethylene glycol monoalkyl ether monoalkyl esterand dipropylene glycol monoalkyl ether monoalkyl ester are preferablyused singly or as a mixture of them.

[0031] Since these compounds have a moderate molecular weight, they havethe safeness and prevent the clogging of nozzles due to the drying ofthe ink composition at the same time. They have no unpleasant odor andtherefore the ink composition comprising such solvents has no unpleasantodor.

[0032] Furthermore, the dipropylene glycol derivatives have bettersafeness and thus more suitable for use in the ink composition than thediethylene glycol derivatives.

[0033] Specific examples of such glycol derivatives include diethyleneglycol monoethyl ether monomethyl ester, diethylene glycol monobutylether monomethyl ester, diproyplene glycol monomethyl ether monomethylester, dipropylene glycol monoethyl ether monomethyl ester, etc.

[0034] The above derivatives are preferably used since they have aparticularly high flash point. In particular, dipropylene glycolmonomethyl ether monomethyl ester is preferable as a solvent of the inkcomposition according to the present invention, since it has a highflash point and low odor.

[0035] Examples of the dialkyl ether of a (poly)alkylene glycol includeethylene glycol dialkyl ether, diethylene glycol dialkyl ether,triethylene glycol dialkyl ether, propylene glycol dialkyl ether,dipropylene glycol dialkyl ether, tripropylene glycol dialkyl ether,etc. They may be used singly or as a mixture of two or more of them.

[0036] Specific examples of such dialkyl ethers of a (poly)alkyleneglycol include ethylene glycol dibutyl ether, diethylene glycol dimethylether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether,propylene glycol dimethyl ether, propylene glycol diethyl ether,propylene glycol dibutyl ether, dipropylene glycol dimethyl ether,dipropylene glycol diethyl ether, etc. These derivatives haveparticularly low odor.

[0037] Among them, (poly)propylene glycol dialkyl ethers are preferablyused as the solvents of the ink composition according to the presentinvention, since they have relatively low odor and a low viscosity.

[0038] Examples of the dialkyl ester of (poly)alkylene glycol includeethylene glycol dialkyl ester, diethylene glycol dialkyl ester,triethylene glycol dialkyl ester, propylene glycol dialkyl ester,dipropylene glycol dialkyl ester, tripropylene glycol dialkyl ester,etc. They may be used singly or as a mixture of two or more of them.

[0039] Preferable examples of such dialkyl esters of a (poly)alkyleneglycol include ethylene glycol dimethyl ester, diethylene glycol,dimethyl ester, propylene glycol dimethyl ester, dipropylene glycoldimethyl ester, etc., since they have low odor.

[0040] Among them, propylene glycol dimethyl ester is preferably used asthe solvent of the ink composition according to the present invention,since it has relatively low odor and a low viscosity.

[0041] The (poly)alkylene glycol derivatives may be used singly or as amixture of two or more of them. One or more (poly)alkylene glycolderivatives are contained in the ink composition in an amount of 30 to90% by weight, preferably 50 to 90% by weight.

[0042] To qualitatively and quantitatively analyze the (poly)alkyleneglycol derivative in the ink composition, gas chromatographic massspectroscopy (GCMS) is advantageously used.

[0043] Optionally, a (poly)alkylene glycol derivative having a flashpoint of lower than 63° C. may be used. Such a (poly)alkylene glycolderivative is used in combination with the other (poly)alkylene glycolderivative in an amount such that the ink composition as a whole has aflash point of at least 63° C. For example, when a (poly)alkylene glycolderivative having a flash point of 50 to 63° C., it is used in an amountof 35% by weight or less, preferably 30% by weight or less based on thewhole weight of the ink composition.

[0044] The ink composition of the present invention contains the(poly)alkylene glycol derivative and the nitrogen-containingheterocyclic compound as the essential organic solvents. Apart fromthese essential organic solvents, the ink composition of the presentinvention may optionally contain other general organic solvents such asalcohols, ketones, esters, amines, glycols, glycol ethers, aromaticcompounds, etc. The kind and amount of such an optional organic solventshould be selected so that the characteristic properties of the inkcomposition of the present invention are not impaired.

[0045] In particular, most of the ketones, esters and aromatic compoundsemit odor even if they are used in a small amount. Therefore, when sucha solvent is used, one having a boiling point of at least 150° C. and aflash point of at least 70° C. is preferably used. Since anorganicsolvent having a boiling point lower than 150° C. emits odor, its amountis preferably less than 1% by weight, more preferably less than 0.5% byweight, most preferably less than 0.1% by weight based on the wholeweight of the ink composition.

[0046] The oil-based pigmented ink composition of the present inventionis characterized in that the composition as a whole has a flash point ofat least 63° C., preferably at least 70° C. by the use of the specificcombination of the organic solvents. When an ink composition has a flashpoint of 62° C. or lower, it is classified into flammable liquids havinga high flash point in the case of dangerous materials to be shippedaccording to international transport-related laws. Therefore, thehandling of such ink compositions is difficult because of the limitationof the transport or transfer. Furthermore, such ink composition maycarry a lot of risk such as firing in the case of troubles, for example,the leakage of the ink composition. In contrast, when the inkcomposition has a flash point of 63° C. or higher, such problems can beavoided. When the ink composition has a flash point of 70° C. or higher,it is designated as Hazardous Material Group IV, Third Petroleum Oil,which is listed in the Appendix to the Fire Defense Law in Japan. Thus,its handling is easy and the dangers such as firing are suppressed, inview of the restrictions encountered in the production, storage,transport and the like.

[0047] The oil-based pigmented ink composition of the present inventioncontains one or more pigments as coloring agents in view of lightstability. The pigments include inorganic pigments and organic pigments.The pigments may be modified to increase the dispersibility thereof. Forexample, modified pigments having a dialkylaminomethyl group ordialkylaminoethylsulfonic acid amide group are preferably used.

[0048] Examples of the inorganic pigment include titanium oxide, Chinesewhite (zinc flower), zinc oxide, lithopone, iron oxide, aluminum oxide,silicon dioxide, kaolinite, montmorillonite, talc, barium sulfate,calcium carbonate, cadmium red, red oxide, molybdenum red, chromevermilion, molybdate orange, chrome yellow, cadmium yellow, yellow ironoxide, chromium oxide, viridian, cobalt green, titanium cobalt green,Paris blue, cobalt chrome green, Armenian blue, ultramarine bluepigment, cobalt blue, cerulean blue, manganese violet, cobalt violet,mica, etc. Also, carbon black comprising acidic, neutral or basic carbonmay be used.

[0049] Examples of the organic pigments include azo pigments, azomethinepigments, polyazo pigments, phthalocyanine pigments, quinacridonepigments, anthraquinone pigments, indigo pigments, thioindigo pigments,quinophthalone pigments, benzimidazolone pigments, isoindoline pigments,isoindolione pigments, etc. In addition, hollow particles of crosslinkedacrylic resins may be used as a pigment.

[0050] Examples of pigments contained in cyan ink compositions includeC.I. Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22 and 60, etc. Inparticular, one or more of C.I. Pigment Blue 15:3 and 15:3 arepreferably used in view of their good weather resistance and coloringpower.

[0051] Examples of pigments contained in magenta ink compositionsinclude C.I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112,122, 123, 168, 184, 202, 209 and 254, C.I. Pigment Violet 19, etc. Inparticular, one or more of C.I. Pigment Red 122, 202, 209 and 254 andC.I. Pigment Violet 19 are preferably used in view of their good weatherresistance and coloring power.

[0052] Examples of pigments contained in yellow ink compositions includeC.I. Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93,95, 97, 98, 109, 110, 114, 120, 128, 129, 130, 138, 139, 147, 150, 151,154, 155, 180, 185, 213, 214, etc. Among them, C.I. Pigment Yellow 74,83, 109, 110, 120, 128, 138, 139, 150, 151, 154, 155, 213 and 214 arepreferably used singly or as a mixture thereof in view of their goodweather resistance.

[0053] Examples of pigments contained in black ink compositions includeHCF, MCF, RCF, LEF and SCF (available from Mitsubishi Chemical Co.,Ltd.), MONARCH and REGAL (available from Cabot, USA), COLOR BLACK,SPECIAL BLACK and PRINTEX (available from Degussa Huls AG), TOKA BLACK(available from TOKAI CARBON Co., Ltd.), RAVEN (available from ColumbianChemical, USA), and the like.

[0054] In particular, one or more of HCF #2650, #2600, #2350 and #2300,MCF #1000, #980, #970 and #960, MCF 88, LFFMA 7, MA 8, MA 11, MA 77 andMA 100 (available from Mitsubishi Chemical Co., Ltd.), and PRINTEX 95,85, 75, 55 and 45 (available from Degussa Huls AG) are preferably used.

[0055] In the oil-based pigmented ink composition of the presentinvention, polymer are used as a pigment-dispersant and/or a fixingresin. The pigment-dispersant has good affinity with the pigment andstabilizes the dispersion of the pigment. The fixing resin has goodadhesion to a substrate and imparts durability to the printed material.

[0056] When the pigment-disperstant and/or the fixing resin areadequately selected depending on the kinds of the pigment, organicsolvents and printing medium, the ink composition has good effects.Among the polymers, a single polymer may act as a pigment-dispersant anda fixing resin.

[0057] The polymer preferably has a solubility in water and ethanol of3% by weight or less, more preferably 1% by weight or less.

[0058] The pigment-dispersant and the fixing resin remain on the surfaceof the substrate after printing with the ink-jet printing system andthen they are dried and fixed to the substrate. Therefore, if thepolymer is easily soluble in water, the printed material has less waterresistance so that the printed characters and/or images are washed offwith rain, when the printed material is used outdoors. When the printedmaterial is used in the form of a poster, a coating agent is oftensprayed on the printed surface. Since the coating agent usually containsan alcoholic solvent as a primary solvent, the printed characters andimages are sagged with the coating agent if the polymers are easilysoluble in the alcoholic solvent.

[0059] In contrast, the polymers having the solubility in water andethanol in the above range do not suffer from such problems.

[0060] As the pigment-dispersant, an ionic or nonionic surfactant, or ananionic, cationic or nonionic polymer is used. In view of the dispersionstability, water resistance and the durability of the printed materialsuch as scratch resistance, etc, the polymer, in particular, a polymerhaving a cationic group or an anionic group is preferable.

[0061] The pigment-dispersant stabilizes the pigment in the organicsolvent through an acid-base interaction between the pigment and thedispersant. Thus, the pigment-dispersant should contain at least one ofa cationic group and an anionic group, which function aspigment-absorbing sites, and the kind and amount of the cationic groupand the anionic group of the dispersant are selected depending on thekind of the pigment.

[0062] Examples of the polymeric pigment-dispersant include SOLSPERSE(available from Zeneca), DISPER BYK (available from BYK-Chemie), EFKA(available from EFKA Additives), etc. Among them, DISPER BYK 161, 162and 168, and EFKA 4050, 4055 and 4060 are preferable. When thesepigment-dispersants are selected and used according to the kinds of thepigment and solvents, the ink composition can often exhibit goodeffects.

[0063] The pigment-dispersants are usually available in the market inthe form of solutions. In such a case, the solution contains alow-boiling solvent such as toluene, xylene, ethyl acetate, butylacetate, methyl ethyl ketone, etc. When the solution is used as such inthe preparation of the ink composition, the ink composition may haveodor originated from such a solvent. Therefore, the low-boiling solventis removed from the solution of the pigment-dispersant, if necessary,when the solvents may have adverse affects on the properties of the inkcomposition, for example, odor, safeness, etc. The low-boiling solventcan be removed by vacuum distillation, reprecipitation, etc.

[0064] By such removal methods, the content of the low-boiling solventin the dispersant solution, in particular, a solvent having a boilingpoint of 170° C. or lower, is decreased to 1% by weight or lower,preferably 0.5% by weight or lower, more preferably 0.1% by weight orlower of the dispersant solution. Thereby, the odor of the inkcomposition can be controlled.

[0065] Examples of the fixing resin include acrylic resins, polyesterresins, polyurethane resins, vinyl chloride resins, cellulose resins(e.g. nitrocellulose), and the like. Most of these resins have goodfixing properties to PVC. The water resistance, dispersion stability,printing properties, etc. can be controlled by selecting the functionalgroups and structures of the resins.

[0066] Examples of the acrylic resin include JOHNCRYL of Johnson Polymerand S-LEK of Sekisui Chemical Co., Ltd. Examples of the polyester resininclude ELITEL of UNITIKA Co., Ltd. and VYLON of Toyobo Co., Ltd.Examples of the polyurethane resin include VYLON UR of Toyobo Co., Ltd.,NT-HiLamic of Dainichi Seika Color & Chemicals Mfg. Co., Ltd., CRISVONof Dainippon Ink and Chemicals Incorporated, and NIPPORAN of NipponPolyurethane Industry Co., Ltd. Examples of the vinyl chloride resininclude SOLBIN of Nissin Chemical Industries, Ltd., SEKISUI PVC-TG andSEKISUI PVC-HA of Sekisui Chemical Co., Ltd., and UCAR Series of DOWCHEMICAL. Examples of nitrocellulose include HIG, LIG, SL and VX ofASAHI CHEMICAL Co., Ltd. and NITROCELLULOSE RS and SS of DAICEL CHEMICALINDUSTRIES, LTD.

[0067] Among them, the polyurethane resins, polyester resins, vinylchloride resins and nitrocellulose are preferable.

[0068] The fixing resin preferably has a weight average molecular weightof 2000 to 100,000, more preferably 5000 to 80,000, most preferably10,000 to 50,000.

[0069] When the weight average molecular weight of the fixing resin isless than 2000, the effect of steric repellence may not be achieved whenthe anionic resin is adsorbed on the pigment particles in the inkcomposition so that the storage stability of the ink composition is notimproved, the fixing of the pigment to the printing medium may not beincreased, and thus the film strength may not be sufficiently attained.When the weight average molecular weight of the fixing resin exceeds100,000, the effects of the use of the fixing resin is saturated andalso the viscosity of the ink composition increases so that the inkcomposition may not have sufficient flowability.

[0070] Herein, the weight average molecular weight means a molecularweight of the resin measured by gel permeation chromatography andcalibrated with standard samples of polystyrene.

[0071] When the polymeric a pigment-dispersant is present in the inkcomposition of the present invention, the amount of thepigment-dispersant may depend on the kinds of the pigment and solventused for dispersing the pigment, the dispersing conditions, etc., and isusually from 5 to 150% by weight, in particular, from 40 to 150% byweight when the organic pigment is used, and from 5 to 60% by weightwhen the inorganic pigment is used, based on the weight of the pigment.

[0072] When the polymeric fixing resin is present in the ink compositionof the present invention, the amount of the fixing resin may depend onthe kind and molecular weight of the resin, the kinds of the pigment andsolvents, and is usually from 5 to 200% by weight based on the weight ofthe pigment.

[0073] The ink composition of the present invention can be prepared byany conventional method. For example, the pigment, the polymer(pigment-dispersant) and the (poly)alkylene glycol derivative as a partof the solvents are premixed and dispersed. Then, to the dispersion, thepolymer (fixing resin), the rest of the (poly)alkylene glycol derivativeand the nitrogen-containing heterocyclic compound are added and mixed todisperse the pigment and the polymers in the solvents.

[0074] To prepare the above dispersion, the components are well stirredand mixed using a barrel-driving type mills (e.g. ball mill, centrifugalmill, planetary mill, etc.), high-speed rotation mills (e.g. sand mill,etc.), medium-agitation mills (e.g. agitated vessel mill, etc.), simpledispersing equipment (e.g. disper, etc.), and the like.

[0075] After the formation of the dispersion, the dispersion mayadditionally be uniformly mixed with a simple stirrer such as athree-one motor, a magnetic stirrer, a disper, a homogenizer, etc.Furthermore, to reduce the particle size of the solid components, thedispersion may optionally be mixed with a dispersing equipment such as abead mill, a high pressure jet mill, etc.

[0076] Besides the pigment, polymers and organic solvents, the inkcomposition of the present invention may optionally containconventionally used additives such as surfactants, surface-modifiers,leveling agents, defoaming agents, antioxidants, pH regulators, chargingagents, disinfectants, preservatives, deodorants, charge-adjusters,wetting agents, anti-skinning agents, UV-ray absorbers, perfumes,pigment derivatives, etc.

[0077] The oil-based pigmented ink of the present invention, inparticular, one for ink-jet printing systems, has a surface tension of20 to 40 mN/m (at 25° C.) and a viscosity of 2 to 15 cp (at 25° C.),preferably 3 to 13 cp, more preferably 4 to 12 cp.

[0078] When the ink composition having the surface tension and viscosityin the above ranges is used in the ink-jet printing system, it has goodjetting properties so that the flying track of an ink drop is not curvedor swerved, and the printed characters or images are not or hardlyblurred, when the ink composition is printed on a plain paper or a mattepaper, etc.

[0079] In the oil-based pigmented ink composition of the presentinvention, the pigment preferably has a dispersion average particle sizeof 20 to 200 nm, more preferably 50 to 160 nm. When the dispersionaverage particle size is less than 20 nm, the particles are too small sothat the printed material may lose the durability. When the dispersionaverage particle size exceeds 200 nm, the fineness of the printedmaterial may deteriorate.

[0080] With the oil-based pigmented ink composition of the presentinvention, the surface tension and viscosity at 25° C. and thedispersion average particle size and maximum dispersion particle size ofthe pigment can be adjusted in the above respective ranges by suitablyselecting the kinds and amounts of the components of the inkcomposition, since the above specific compounds are used as the organicsolvents.

[0081] The oil-based pigmented ink composition of the present inventionhas low odor and high safeness, is printable on various printing mediasuch as an inexpensive film of PVC having no receptive layer and canendure the outdoor use conditions. Furthermore, the oil-based pigmentedink composition of the present invention is advantageously used in theink-jet printing systems. In such systems, the four or more inkcompositions including the cyan, magenta, yellow and black inkcompositions can be used at the same time to form images.

EXAMPLES

[0082] Hereinafter, the present invention will be illustrated by thefollowing examples, in which “parts” means “parts by weight” unlessotherwise indicated.

[0083] In the Examples, a pigment-dispersant “BYK 161” and a fixingresin “Vylon UR-8300” were used after removing low boiling solvents byvacuum distillation and then diluting them with organic solvents to beused in a dispersing step to a solid content of 20% by weight.

[0084] In the Examples, the amounts of pigment-dispersants “BYK 161” and“SOLSPERSE 13940” and a fixing resin “Vylon UR 8300” are expressed interms of weights after being diluted with organic solvents.

Example 1

[0085] In a 100 cc plastic bottle, 4 parts of a copper phthalocyanineblue pigment (“FASTOGEN BLUE 5430SD” available from Dainippon Ink andChemicals Incorporated), 10 parts of a pigment-dispersant (“BYK 161”, anamine-based polymeric dispersant, available from BYK-Chemie), 6 parts ofdipropylene glycol monomethyl ether monomethyl ester (available from DowChemical; flash point: 96° C.) as an organic solvent and 100 parts ofzirconia beads having a diameter of 0.3 mm were weighed and charged.Then, the mixture was dispersed with a paint conditioner (available fromTOYO SEIKI KOGYO Co., Ltd.) for 2 hours.

[0086] Then, 7.5 parts of the dispersion prepared in the previous step,3.8 parts of a polyurethane resin (“Vylon UR 8300” available from TOYOBOCo., Ltd.), 10 parts of N-methyl-2-pyrrolidone, 18.7 parts ofdipropylene glycol monomethyl ether monomethyl ester and 10 parts ofdipropylene glycol dimethyl ether (available from Dow Chemical; flashpoint: 60° C.) were added, and the mixture was stirred with a magneticstirrer for 30 minutes. Thereafter, the mixture was suction filtratedthrough a glass filter (available from KIRIYAMA GLASS WORKS Co., Ltd.)to obtain an oil-based pigmented ink composition (hereinafter referredto as Ink Composition A).

Example 2

[0087] A dispersion was prepared in the same manner as in Example 1except that a quinacridon pigment (“HOSTAPERM PINK EB trans” availablefrom Clariant AG) was used in place of the copper phthalocyaninepigment, and 20 parts of the pigment-dispersant “BYK 161” and 6 parts ofdipropylene glycol monomethyl ether monomethyl ester were used. Then,using this dispersion, an oil-based pigmented ink composition (InkComposition B) was prepared in the same manner as in Example 1.

Example 3

[0088] A dispersion was prepared in the same manner as in Example 1except that an azo pigment (“NOVOPERM Yellow H2G” available fromClariant AG) was used in place of the copper phthalocyanine pigment.Then, using this dispersion, an oil-based pigmented ink composition (InkComposition C) was prepared in the same manner as in Example 1.

Example 4

[0089] A dispersion was prepared in the same manner as in Example 1except that an acidic carbon black pigment (“MA 8” available fromMITSUBISHI CHEMICAL CORPORATION) was used in place of the copperphthalocyanine pigment. Then, using this dispersion, an oil-basedpigmented ink composition (Ink Composition D) was prepared in the samemanner as in Example 1.

Example 5

[0090] A dispersion was prepared in the same manner as in Example 2except that a quinacridon pigment (“Chromofine Magenta 6887” availablefrom Dainichi Seika Color & Chemicals Mfg. Co., Ltd.) was used in placeof the quinacridone pigment “HOSTAPERM PINK EB trans”.

[0091] Then, to 7.5 parts of the dispersion prepared in the previousstep, 0.6 part of nitrocellulose (“RS 1/4” available from DAICELCHEMICAL INDUSTRIES, LTD.), 10 parts of N-methyl-2-pyrrolidone, 21.9parts of dipropylene glycol monomethyl ether monomethyl ester and 10parts of dipropylene glycol dimethyl ether were added, and the mixturewas stirred with a magnetic stirrer for 30 minutes. Thereafter, themixture was suction filtrated through a glass filter to obtain anoil-based pigmented ink composition (Ink Composition E).

Example 6

[0092] A dispersion was prepared in the same manner as in Example 1except that an azo pigment (“YELLOW PIGMENT E4GN-GT” available fromBayer AG) was used in place of the copper phthalocyanine pigment, and 20parts of the pigment-dispersant “BYK 161” and 6 parts of dipropyleneglycol monomethyl ether monomethyl ester were used.

[0093] Then, to 7.5 parts of the dispersion prepared in the previousstep, 0.8 part of a polyester resin (“ELITEL UE-9800” available fromUNITIKA Co., Ltd.; weight average molecular weight: 13,000), 10 parts ofN-methyl-2-pyrrolidone, 21.7 parts of dipropylene glycol monomethylether monomethyl ester, and 10 parts of dipropylene glycol dimethylether were added, and the mixture was stirred with a magnetic stirrerfor 30 minutes. Thereafter, the mixture was suction filtrated through aglass filter to obtain an oil-based pigmented ink composition (InkComposition F).

Example 7

[0094] A dispersion was prepared in the same manner as in Example 1except that a basic carbon black pigment (“Printex 85” available fromDEGUSSA HULS) was used in place of the copper phthalocyanine pigment,and propylene glycol dimethyl ether (available from Dow Chemical; flashpoint: 93° C.) was used in place of dipropylene glycol monomethyl ethermonomethyl ester.

[0095] Then, to 7.5 parts of the dispersion prepared in the previousstep, 0.5 part of a polyester resin (“Vylon 296” available from TOYOBOCo., Ltd.; weight average molecular weight: 14,000), 10 parts ofN-methyl-2-pyrrolidone, and 32 parts of diethylene glycol dibutyl ether(available from KYOWA HAKKO KOGYO Co., Ltd.; flash point: 122° C.) wereadded, and the mixture was stirred with a magnetic stirrer for 30minutes. Thereafter, the mixture was suction filtrated through a glassfilter to obtain an oil-based pigmented ink composition (Ink CompositionG).

Example 8

[0096] A dispersion was prepared in the same manner as in Example 1except that an amine-based polymer dispersant “BYK 168” (available fromBYK-Chemie) was used in place of “BYK 161”.

[0097] Then, to 7.5 parts of the dispersion prepared in the previousstep, 1.1 parts of a vinyl chloride-vinyl acetate copolymer (“VROH”available from Dow Chemical; weight average molecular weight: 15,000),10 parts of N-methyl-2-pyrrolidone, 19.4 parts of dipropylene glycolmonomethyl ether monomethyl ester and 12 parts of dipropylene glycoldimethyl ether (available from Dow Chemical; flash point: 60° C.) wereadded, and the mixture was stirred with a magnetic stirrer for 60minutes. Thereafter, the mixture was suction filtrated through a glassfilter to obtain an oil-based pigmented ink composition (Ink CompositionH).

Example 9

[0098] A dispersion was prepared in the same manner as in Example 1except that ethylene glycol monobutyl ether monoethyl ester (availablefrom KYOWA HAKKO KOGYO Co., Ltd.; flash point: 87.5° C.; boiling point:192° C.) was used in place of dipropylene glycol monomethyl ethermonomethyl ester.

[0099] Then, to 7.5 parts of the dispersion prepared in the previousstep, 3.8 parts of a polyurethane resin (“Vylon UR 8300” available fromTOYOBO Co., Ltd.), 10 parts of N-methyl-2-pyrrolidone, 23.7 parts ofethylene glycol monobutyl ether monomethyl ether, and 5 parts ofdipropylene glycol monomethyl ether monomethyl ester were added, and themixture was stirred with a magnetic stirrer for 30 minutes. Thereafter,the mixture was suction filtrated through a glass filter to obtain anoil-based pigmented ink composition (Ink Composition I).

Example 10

[0100] A dispersion was prepared in the same manner as in Example 1except that an azo pigment (“YELLOW PIGMENT E4GN-GT” available fromBayer AG) was used in place of the copper phthalocyanine pigment, and 10parts of a pigment-dispersant “BYK 168” was used in place of “BYK 161”.

[0101] Then, to 7.5 parts of the dispersion prepared in the previousstep, 0.8 part of a vinyl chloride-vinyl acetate copolymer (“SOLBINTA5R” available from NISSIN CHEMICAL Co., Ltd.; weight average molecularweight: 28,000), 10 parts of N-ethyl-2-pyrrolidone, 19.7 parts ofdipropylene glycol monomethyl ether monomethyl ester, and 12 parts ofdipropylene glycol dimethyl ether were added, and the mixture wasstirred with a magnetic stirrer for 30 minutes. Thereafter, the mixturewas suction filtrated through a glass filter to obtain an oil-basedpigmented ink composition (Ink Composition J).

Example 11

[0102] To 7.5 parts of the dispersion prepared in the same manner as inExample 1, 3.8 parts of “Vylon UR 8300”, 5 parts ofN-methyl-2-pyrrolidone, 23.7 parts of dipropylene glycol monomethylether monomethyl ester, and 10 parts of dipropylene glycol dimethylether were added, and the mixture was stirred with a magnetic stirrerfor 30 minutes. Thereafter, the mixture was suction filtrated through aglass filter to obtain an oil-based pigmented ink composition (InkComposition K).

Example 12

[0103] To 7.5 parts of the dispersion prepared in the same manner as inExample 1, 3.8 parts of “Vylon UR 8300”, 15 parts ofN-methyl-2-pyrrolidone, 13.7 parts of dipropylene glycol monomethylether monomethyl ester, and 10 parts of dipropylene glycol dimethylether were added, and the mixture was stirred with a magnetic stirrerfor 30 minutes. Thereafter, the mixture was suction filtrated through aglass filter to obtain an oil-based pigmented ink composition (InkComposition L).

Comparative Example 1

[0104] Oil-Based Pigmented Ink Composition Comprising 50% by Weight ormore of (poly)alkylene glycol Derivative Having a Flash Point Lower than50° C.

[0105] A dispersion was prepared in the same manner as in Example 1except that propylene glycol monomethyl ether monoethyl ether having aflash point of 46.5° C. (available from KYOWA HAKKO KOGYO Co., Ltd.) wasused in place of dipropylene glycol monomethyl ether monomethyl ester.

[0106] Then, to 7.5 parts of the dispersion prepared in the previousstep, 3.8 parts of “Vylon UR 8300”, 10 parts of N-methyl-2-pyrrolidone,18.7 parts of propylene glycol monomethyl ether monomethyl ester, and 10parts of dipropylene glycol monomethyl ether monomethyl ester wereadded, and the mixture was stirred with a magnetic stirrer for 30minutes. Thereafter, the mixture was suction filtrated through a glassfilter to obtain an oil-based pigmented ink composition (Ink CompositionM).

Comparative Example 2

[0107] Oil-Based Pigmented Ink Composition Comprising a Hydrocarbon as aPrimary Solvent

[0108] A dispersion was prepared in the same manner as in Example 1except that an aliphatic hydrocarbon solvent (“ISOPER G” available fromExxon Chemical) was used in place of dipropylene glycol monomethyl ethermonomethyl ester, and an amine-based polymer dispersant (“SOLSPERSE13940” available from Zeneca) was used as a pigment-dispersant.

[0109] Then, the ink composition was prepared in the same manner as inExample 1 except that 10 parts of N-dimethyl-2-pyrrolidone and 28 partsof “ISOPER G” were added to 10 parts of the dispersion prepared in theprevious step.

Comparative Example 3

[0110] Oil-Based Pigmented Ink Composition 1 Containing noN-alkyl-2-pyrrolidone

[0111] To 7.5 parts of the dispersion prepared in the same manner as inExample 1, 0.8 part of nitrocellulose (“RS 1/4” available from DAICELCHEMICAL INDUSTRIES, LTD.), 31.7 parts of dipropylene glycol monomethylether monomethyl ester, and 10 parts of dipropylene glycol dimethylether were added, and the mixture was stirred with a magnetic stirrerfor 30 minutes. Thereafter, the mixture was suction filtrated through aglass filter to obtain an oil-based pigmented ink composition (InkComposition 0).

Example 4

[0112] Oil-Based Pigmented Ink Composition 2 Containing noN-alkyl-2-pyrrolidone

[0113] A dispersion was prepared in the same manner as in Example 1except that ethylene glycol monobutyl ether monomethyl ester was used inplace of dipropylene glycol monomethl ether monomethyl ester.

[0114] Then, to 7.5 parts of the dispersion prepared in the previousstep, 1 part of a polyester resin (“Vylon 200” available from TOYOBOCo., Ltd.), and 41.5 parts of ethylene glycol monobutyl ether monomethylester were added, and the mixture was stirred with a magnetic stirrerfor 60 minutes. Thereafter, the mixture was suction filtrated through aglass filter to obtain an oil-based pigmented ink composition (InkComposition P).

Comparative Example 5

[0115] Oil-Based Pigmented Ink Composition 3 Containing noN-alkyl-2-pyrrolidone

[0116] A dispersion was prepared in the same manner as in Example 1except that an acidic carbon black (“MA 100” available from MitsubishiChemical Co., Ltd.) was used in place of the copper phthalocyaninepigment, diethylene glycol monobutyl ether monomethyl ester (flashpoint: 124° C.; boiling point: 247° C.) was used in place of dipropyleneglycol monomethyl ether monomethyl ester, and 2.0 parts of an anionicsurfactant (“HOMOGENOL L-95” available from KAO Corporation) was used asa pigment-dispersant.

[0117] Then, to 16.25 parts of the dispersion prepared in the previousstep, chlorinated polyethylene (“HE-510” available from Nippon PaperIndustries Co., Ltd.), and 29.5 parts of diethylene glycol monobutylether monomethyl ester as an organic solvent were added. Thereafter, anink composition (Ink Composition Q) was prepared in the same manner asin Example 1.

Comparative Example 6

[0118] Oil-Based Pigmented Ink Composition 1 Containing no(poly)alkylene glycol Derivative

[0119] A dispersion was prepared in the same manner as in Example 1except that a quinacridon pigment (“PV Fast Red E5B” available fromClariant AG) was used in place of the copper phthalocyanine pigment,propylene carbonate (flash point: 132° C.; boiling point: 242° C.) wasused in place of dipropylene glycol monomethyl ether monomethyl ester,and 2.0 parts of “HOMOGENOL L-95” was used as a pigment-dispersant.

[0120] Then, to 16.25 parts of the dispersion prepared in the previousstep, 4.25 parts of nitrocellulose (“SL-1” available from Asahi ChemicalCo., Ltd.), and 29.5 parts of propylene carbonate as an organic solventwere added. Thereafter, an ink composition (Ink Composition R) wasprepared in the same manner as in Example 1.

Comparative Example 7

[0121] Oil-Based Pigmented Ink Composition 2 Containing no(poly)alkylene glycol Derivative

[0122] A dispersion was prepared in the same manner as in ComparativeExample 6 except that cyclohexanone (flash point: 44° C.; boiling point:156° C.) was used in place of propylene carbonate.

[0123] Then, to 16.25 parts of the dispersion prepared in the previousstep, 8.5 parts of “Vylon 200”, and 29.5 parts of cyclohexanone as anorganic solvent were added. Thereafter, an ink composition (InkComposition S) was prepared in the same manner as in Example 1.

Comparative Example 8

[0124] Aqueous Pigmented Ink Composition Containing Water andN-methyl-2-pyrrolidone as Solvents

[0125] In a 100 cc plastic bottle, 4 parts of a copper phthalocyanineblue pigment (“FASTOGEN BLUE 5430SD” available from Dainippon Ink andChemicals Incorporated), 6 parts of a pigment-dispersant (“JOHNCRYL”available from JOHNSON POLYMER CORPORATION), 10 parts of a mixture ofion-exchanged water and triethylene glycol (90:10 by weight), and 100parts of zirconia beads having a diameter of 3 mm were weighed andcharged. Then, the mixture was dispersed with a paint conditioner(available from TOYO SEIKI KOGYO Co., Ltd.) for 2 hours.

[0126] Then, to 7.5 parts of the dispersion prepared in the previousstep, 10 parts of N-methyl-2-pyrrolidone, and 22.5 parts ofion-exchanged water were added, and the mixture was stirred with amagnetic stirrer for 30 minutes. Thereafter, the mixture was suctionfiltrated through a glass filter to obtain an aqueous pigmented inkcomposition (Ink Composition T).

[0127] With Ink Compositions A to L of Examples 1-12, Ink Compositions Mto S of Comparative Examples 1-7, and Ink Composition T of ComparativeExample 8, a viscosity, a surface tension, a dispersion average particlesize and a flash point were measured by the methods described below. Theresults are shown in Table 1.

[0128] Viscosity:

[0129] A viscosity of an ink composition was measured using a R100viscometer (available from TOKI SANGYO Co., Ltd.) at 25° C. and a conerotation speed of 20 rpm.

[0130] Surface Tension:

[0131] A surface tension of an ink composition was measured using afull-automatic balance type electrotensiometer ESB-V (available fromKYOWA SCIENCE Co., Ltd.) at an ink temperature of 25° C.

[0132] Dispersion Average Particle Size:

[0133] A dispersion average particle size of pigment particles wasmeasured using a particle size analyzer N4-PLUS (a laser Dopplerparticle size analyzer available from Coulter).

[0134] Flash Point:

[0135] A flash point was measured using a SETA sealed flash pointtester. TABLE 1 Dispersion Ink Surface average Flash Example composi-Viscosity tension particle point No. tion (cp) (mN/m) size (nm) (° C.)Ex. 1 A 4.5 29.0 98 74 Ex. 2 B 5.0 28.8 128 75 Ex. 3 C 4.3 29.1 135 74Ex. 4 D 4.2 28.8 105 75 Ex. 5 E 5.2 28.8 110 74 Ex. 6 F 4.9 29.3 158 75Ex. 7 G 5.6 29.5 139 102 Ex. 8 H 4.7 28.8 118 71 Ex. 9 I 4.2 28.2 104 72Ex. 10 J 5.2 28.9 148 71 Ex. 11 K 4.4 28.7 99 73 Ex. 12 L 4.7 29.3 10175 C. Ex. 1 M 3.8 26.9 104 55 C. Ex. 2 N 4.0 23.2 135 43 C. Ex. 3 O 4.128.4 116 75 C. Ex. 4 P 3.2 29.5 115 48 C. Ex. 5 Q 11.8 29.0 187 124 C.Ex. 6 R 11.5 35.0 195 132 C. Ex. 7 S 3.5 36.5 138 43 C. Ex. 8 T 3.1 36.5128 —

[0136] As can be seen from the results in Table 1, the oil-basedpigmented ink compositions A to L according to the present invention hasadequate viscosities, surface tensions and dispersion average particlesizes, and also they have a flash point of 70° C. or higher, so thatthey are designated as Hazardous Material Group IV, Third Petroleum Oil,water-insoluble liquid, which is listed in the Appendix to the FireDefense Law in Japan, and can be relatively safely handled.

[0137] In contrast, oil-based pigmented ink compositions M, N, P and Sof Comparative Examples 1, 2, 4 and 7 had a flash point lower than 70°C., so that they are designated as Hazardous Material Group IV, SecondPetroleum Oil, water-insoluble liquid. Thus, such compositions should becarefully handled and their storage and transportation are restricted.

[0138] Next, with Ink Compositions A to L of Examples 1-12, InkCompositions M to S of Comparative Examples 1-7, and Ink Composition Tof Comparative Example 8, a drying property, a fixing property, alcoholresistance and odor were evaluated by the methods described below. Theresults are shown in Table 2.

[0139] Drying Property:

[0140] An ink composition was coated on a glossy PVC sheet (P-224RWavailable from LINTEC Corporation) with a No. 6 wire bar (available fromTOYO SEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C.and 30% RH, and its drying property was evaluated according to thefollowing criteria:

[0141] A: When the coated composition is touched with a finger, thecoated composition does not adhere to the finger within one minutedrying.

[0142] B: When the coated composition is touched with a finger, thecoated composition does not adhere to the finger within 5 minutesdrying.

[0143] C: When the coated composition is touched with a finger, thecoated composition still adheres to the finger after 5 minutes drying.

[0144] Fixing Property:

[0145] An ink composition was coated on a glossy PVC sheet (P-224RWavailable from LINTEC Corporation) with a No. 6 wire bar (available fromTOYO SEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C.and 30% RH, and kept standing for 1 hour. After that, the surface of thecoated ink composition was scrubbed with a finger for 30 seconds. Then,the fixing property was evaluated according to the following criteria:

[0146] A: No scrubbed mark was observed.

[0147] B: A small number of scrubbed marks were observed.

[0148] C: Scrubbed marks were generated and the substrate PVC sheet wasexposed.

[0149] Alcohol Resistance:

[0150] An ink composition was coated on a glossy PVC sheet (P-224RWavailable from LINTEC Corporation) with a No. 6 wire bar (available fromTOYO SEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C.and 30% RH, and kept standing for 1 hour. After that, the surface of thecoated ink composition was wiped with a piece of cloth (BENCOTTONavailable from ASAHI CHEMICAL Co., Ltd.) soaked with a water/ethanolmixture (weight ratio of 1:1). Then, the alcohol resistance wasevaluated according to the following criteria:

[0151] A: The surface of the coated ink composition was not wiped off.

[0152] B: When the surface of the coated ink composition was stronglywiped, the color was slightly faded.

[0153] C: The coated ink composition was easily wiped off and thesubstrate PVS sheet was exposed.

[0154] Odor:

[0155] An ink composition was coated on a glossy PVC sheet (P-224RWavailable from LINTEC Corporation) with a No. 6 wire bar (available fromTOYO SEIKI KOGYO Co., Ltd.) in a temperature-controlled room at 25° C.and 30% RH, and kept standing for 10 minutes. Then, the odor from thecoated ink composition was smelled and evaluated according to thefollowing criteria:

[0156] A: Substantially no odor was smelled.

[0157] B: Slight odor was smelled.

[0158] C. Unpleasant odor was smelled. TABLE 2 Ink Example composi-Drying Fixing Alcohol No. tion property property resistance Odor Ex. 1 AA A A A Ex. 2 B A A A A Ex. 3 C A A A A Ex. 4 D A A A A Ex. 5 E A A A AEx. 6 F A A A A Ex. 7 G A A A A Ex. 8 H A A A A Ex. 9 I A A A B Ex. 10 JA A A A Ex. 11 K B A B A Ex. 12 L B A A A C. Ex. 1 M A A A C C. Ex. 2 NC C C B C. Ex. 3 O B B B A C. Ex. 4 P B A C B C. Ex. 5 Q C C C A C. Ex.6 R C C C A C. Ex. 7 S A A A C C. Ex. 8 T C C C A

[0159] As can be seen from the results of Table 2, oil-based pigmentedink compositions A to L of Examples 1 to 12 had good drying property,fixing property and alcohol resistance, and had problem-free printingproperty on PVC.

[0160] Among oil-based pigmented ink compositions A to L of Examples 1to 12, ink composition I of Example 9 emitted slight odor and may have asmall trouble when used in a printer. However, ink compositions A to Hand J to L of Examples 1-8 and 10 to 12 emit substantially no odor andcause no problem when used in a printer.

[0161] Since ink composition K of Example 11 contained a small amount ofN-methyl-2-pyrrolidone, it slowly interfused in PVC, had a slightly lowdrying property and did not largely dissolve PVC. Accordingly, itsalcohol resistance was not good. Ink composition L of Example 12containing a relatively large amount of N-methyl-2-pyrrolidone has goodfixing property to PVC, but N-methyl-2-pyrrolidone, which shouldinterfuse in PVC, was saturated and remained on the surface, so that itsdrying property was less satisfactory.

[0162] In contrast, ink composition M and S of Examples 1 and 7 had noproblem in printing property on PVC. However, since they contained thelow-boiling solvent, they had a small problem of odor so that it maycause some trouble when used in a printer. These ink compositions had aflash point of lower than 62° C. as described above. Thus, their storageand transportation are restricted.

[0163] Ink composition N and T of Comparative Examples 2 and 8comprising the hydrocarbon solvent did not emit odor, but had no fixingproperty on PVC and the ink compositions were repelled.

[0164] Furthermore, ink compositions 0 and P of Comparative Examples 3and 4, which contained no N-alkyl-2-pyrrolidone, had relatively lowdrying property since they contained no solvent that dissolves the PVCsubstrate, and they had inferior fixing property and alcohol resistanceto the ink compositions of Examples 1 to 12.

[0165] Ink composition Q of Comparative Example 5 containing noN-alkyl-2-pyrrolidone and ink composition R of Comparative Example 6containing neither N-alkyl-2-pyrrolidone nor (poly)alkylene glycolderivative contained the high-boiling solvent so that they had noproblem in their odor. However, they had low drying property and did notinterfuse in the PVC substrate. Thus, the solvents remained on thesurface of the PVC substrate, and the ink composition had poor fixingproperty and alcohol resistance.

1. An oil-based pigmented ink composition comprising a pigment, apolymer and an organic solvent, wherein the organic solvent contains a(poly)alkylene glycol derivative in an amount of 30 to 90% by weight anda nitrogen-containing heterocyclic compound in an amount of 1 to 30% byweight, each based on the whole weight of the ink composition, and theink composition has a flash point of at least 63° C.
 2. The oil-basedpigmented ink composition according to claim 1, wherein saidnitrogen-containing heterocyclic compound is a N-alkyl-2-pyrrolidone. 3.The oil-based pigmented ink composition according to claim 2, whereinsaid N-alkyl-2-pyrrolidone is at least one of N-methyl-pyrrolidone andN-ethyl-2-pyrrolidone.
 4. The oil-based pigmented ink compositionaccording to claim 1, wherein said (poly)alkylene glycol derivative hasa flash point of 70 to 120° C., and a boiling point of 170 to 250° C. 5.The oil-based pigmented ink composition according to claim 1, whereinsaid (poly)alkylene glycol derivative is at least one compound selectedfrom the group consisting of monoalkyl ether monoalkyl esters, dialkylethers and dialkyl esters of (poly)alkylene glycols.
 6. The oil-basedpigmented ink composition according to claim 5, wherein said(poly)alkylene glycol derivative is at least one compound selected fromthe group consisting of ethylene glycol monoalkyl ether monoalkyl ester,diethylene glycol monoalkyl ether monoalkyl ester, triethylene glycolmonoalkyl ether monoalkyl ester, propylene glycol monoalkyl ethermonoalkyl ester, dipropylene glycol monoalkyl ether monoalkyl ester,tripropylene glycol monoalkyl ether monoalkyl ester, ethylene glycoldialkyl ether, diethylene glycol dialkyl ether, propylene glycol dialkylether, dipropylene glycol dialkyl ether, ethylene glycol dialkyl esterand propylene glycol dialkyl ester.
 7. The oil-based pigmented inkcomposition according to claim 1, wherein said polymer has a solubilityin water and ethanol of 3% by weight or less.
 8. The oil-based pigmentedink composition according to claim 1, wherein said polymer is at leastone of a pigment-dispersant and a fixing resin.
 9. The oil-basedpigmented ink composition according to claim 8, wherein saidpigment-dispersant is contained in an amount of 5 to 150% by weightbased on the weight of the pigment.
 10. The oil-based pigmented inkcomposition according to claim 8, wherein said fixing resin is at leastone resin selected from the group consisting of acrylic resins,polyester resins, polyurethane resins, vinyl chloride resins andcellulose resins.
 11. The oil-based pigmented ink composition accordingto claim 8, wherein said fixing resin has a weight average molecularweight of 2,000 to 100,000.
 12. The oil-based pigmented ink compositionaccording to claim 8, wherein said fixing resin is contained in anamount of 5 to 200% by weight based on the weight of the pigment. 13.The oil-based pigmented ink composition according to any one of claims 1to 12, which has a viscosity of 2 to 15 cp at 25° C., a surface tensionof 20 to 40 mN/m at 25° C., and a dispersion average particle size of 20to 200 nm.
 14. The oil-based pigmented ink composition according toclaim 1, which is used in an ink-jet printing system.